With the rapid progress of semiconductor industries, the integrated circuits (ICs) used in electronic apparatuses are developed toward minimization, high operating speed and increasing integration level. Due to the reduced size and the increased performance, power semiconductor devices such as power transistors have achieved a great deal of advance. The power transistors are widely used in many electronic apparatuses such as control equipment, measuring equipment, electrical apparatuses and computer peripheral devices because they are very suitable to process high-power signals. During operation of the electronic apparatus, the power transistors may generate energy in the form of heat, which is readily accumulated and difficult to dissipate away. If no proper heat-dissipating mechanism is provided to transfer enough heat to the ambient air, the elevated operating temperature may result in damage of the electronic components, a breakdown of the whole electronic apparatus or reduced operation efficiency. Therefore, it is important to dissipate the heat generated from the power transistors in order to stabilize the operation and extend the operational life of the electronic apparatus.
Typically, the power transistors are fastened onto a surface of a heat sink in order to increase heat-dissipating efficiency. FIG. 1 is a schematic exploded view illustrating a power transistor to be fastened onto a heat sink. FIG. 2 is a schematic cross-sectional view illustrating the assembled structure of the power transistor and the heat sink. By means of a screw 11, a washer 17 and a nut 18, a power transistor 13 is fastened onto a heat sink 16. By means of a plastic bushing 12, an insulating piece 14 and an isolating piece 15, the metallic portion 131 of the power transistor 13 is separated from the screw 11 and the heat sink 16 in order to prevent spark generation and short-circuit breakdown.
Since electronic apparatuses are developed toward minimization, high-density mounting is needed. After the power transistor 13 is fastened onto the heat sink 16, the head portion 111 of the screw 11 is not covered by the plastic bushing 12 and exposed outsides. If the electronic apparatus is suffered from a drop or a strong impact, the head portion 111 of the screw 11 is possibly in contact with adjacent electronic components. In this circumstance, the electronic apparatus will be short-circuited or even damaged.
For solving the above problem, an insulating piece is manually placed in the vicinity of the screw 11 to isolate the screw 11 from other electronic components. Since the insulating piece is not suitably positioned, the insulating piece is readily detached from the original position if the electronic apparatus is suffered from a drop or a strong impact. That is, the head portion 111 of the screw 11 may be still in contact with adjacent electronic components. In addition, manually positioning the insulating piece is labor-intensive and time-consuming.
In views of the above-described disadvantages resulted from the prior art, the applicant keeps on carving unflaggingly to develop an assembled structure of a power semiconductor device and a heat sink according to the present invention through wholehearted experience and research.